London's new Routemaster bus is, for the most part, wonderful. Futuristic in design but retaining the "hop-on" curvy look of the traditional London double decker, it's also a hybrid vehicle which results in far more green-friendly journeys.

But, in the summer, riding the fleet is comparable to being fired in a tin can directly into the sun. They are just too, too hot. Unlike most buses, the top deck windows cannot be opened, creating a stifling, unbearable heat. Though an air cooling system is installed, it's pitiful, barely countering the outside heat. And while the buses are equipped with a second rear door which could aid air flow, drivers (often lacking the second staff member needed to man the door) often leave them closed.

They essentially become a sauna on wheels. Taking stats about an average car with its windows closed in the sun as a comparison, if the outside temperature is hovering around the 32°C mark, within an hour the inside temperature of the vehicle can go as high as 56°C.

Today is expected to be the hottest day of the year, hitting highs of 35°C. So, factor in packed-in passengers (the buses have a capacity of 87 – don't even get started on the sweaty smells) and you could see temperatures soar to obscene levels, likely breaking the legal limit for transporting cattle.

Complaints dating back near the time of the introduction of the buses, petitioning a change in the window system seems, to have fallen on deaf ears at City Hall. Here are just a few Tweets from the past few days (keeping in mind that today is expected to be even hotter), complaining about the heat on the buses: